This disclosure relates to a method for recovering valuable compounds from a waste generated from a diaryl carbonate manufacturing process.
Diaryl carbonates, such as diphenyl carbonate are an important reactant in the production of polycarbonate resins. As the use of polycarbonate resins has increased, the efficient production of diaryl carbonate has become more important. The transesterification method for diaryl carbonate production involves two reaction steps. First, a dialkyl carbonate reacts with an aromatic alcohol to produce an alkyl aryl carbonate and an alkyl alcohol in presence of a transesterification catalyst. Next, two molecules of the alkyl aryl carbonate undergo a disproportionation reaction to produce one molecule of diaryl carbonate and one molecule of dialkyl carbonate. Diaryl carbonates can also be produced by reacting phenol with phosgene.
The waste streams from the diaryl carbonate manufacturing process require special handling for disposal. The waste streams may comprise a variety of compounds such as diaryl carbonate, aromatic alcohol, aromatic salicylate, polycarbonate oligomers, transesterification catalyst and other high boiling compounds. Currently there is no process to efficiently recover these compounds from a waste stream.
Polycarbonate scrap (i.e., polycarbonate waste from manufacturing processes) can be reacted with alcohols to recover monomers. Aromatic alcohol may be recovered from aromatic salicylate by reacting the aromatic salicylate with an alcohol. The products of both recovery processes need to be further purified to be reused for any other synthesis.
This process is different from recovering compounds from a diaryl carbonate process waste stream. Accordingly, there is a need for waste handling process, which can recover valuable compounds from a diaryl carbonate manufacturing waste stream.